1. Field of the Invention
This invention relates to an improvement in a flexible magnetic disk.
2. Description of the Prior Art
Flexible magnetic disks comprising a jacket and a flexible magnetic disk sheet housed therein are commonly used for magnetic recording and reproducing. The jacket and the sheet have circular holes at the centers thereof for engagement with sheet positioning members of an information writing apparatus or an information read-out apparatus. Thus the sheet is rotated by a rotatable section of the sheet positioning members for magnetically recording information in the sheet or for magnetically reproducing information from the sheet. In the magnetic disk of this type, since the sheet is housed in the jacket in slightly spaced relation from the inner surfaces of the jacket, the position of the sheet sometimes comes to be displaced from the center of the jacket during storage, handling or carrying of the magnetic disk. When the magnetic disk is loaded into a writing apparatus or a read-out apparatus in this condition, the circular hole at the center of the sheet is positioned eccentrically with respect to the sheet positioning members (collet and rotatable section) of the apparatus. Thus the sheet is held in an eccentric position, and it becomes impossible to correctly write information into the sheet or to correctly read information out of the sheet.
FIG. 1A is a plan view showing an example of the flexible magnetic disk, and FIG. 1B is a sectional view of the flexible magnetic disk shown in FIG. 1A. The flexible magnetic disk comprises a rectangular jacket 1 having a circular aperture 1a in the center, and a flexible magnetic disk sheet 2 having a circular hole 2a in the center. The magnetic disk sheet 2 is rotatably housed in the jacket 1 so that the peripheral edge portion of the circular hole 2a is exposed within the circular aperture 1a of the jacket 1.
FIG. 2 is a partially sectional view showing the condition of loading the flexible magnetic disk between sheet positioning members in a writing apparatus or a read-out apparatus. FIG. 3 is a partially sectional view showing the condition of the flexible magnetic disk sheet of the flexible magnetic disk held in an eccentric position with respect to the sheet positioning members in a writing apparatus or a read-out apparatus. FIG. 4 is a partially sectional view showing the condition of the flexible magnetic disk sheet of the flexible magnetic disk correctly positioned by the sheet positioning members in a writing apparatus or a read-out apparatus.
As shown in FIG. 2, when the flexible magnetic disk is loaded into a writing apparatus or a read-out apparatus, a rotatable section 3 of the sheet positioning members is contacted with the magnetic disk sheet 2 from below, and a collet 4 of the sheet positioning members is moved down and fitted into a circular recess 3a of the rotatable section 3. However, the peripheral edge portion of the circular hole 2a of the sheet 2 is not always aligned with the peripheral edge portion of the circular recess 3a of the rotatable section 3, but instead is often displaced from the peripheral edge portion of the circular recess 3a. As shown in FIG. 3, when the collet 4 is moved down in this condition, a part of the peripheral edge portion of the circular hole 2a of the sheet 2 is sandwiched between the collet 4 and the peripheral edge portion of the circular recess 3a of the rotatable section 3. As a result, the sheet 2 is held eccentrically with respect to the rotatable section 3 and the collet 4, and rotated in this condition in the writing apparatus or in the read-out apparatus. Such positioning of the sheet 2 must be avoided since writing of information into the sheet 2 and read-out of information therefrom are not conducted correctly unless the sheet 2 is rotated with the center thereof exactly aligned with the rotation axis. Further, when the sheet 2 is rotated in the eccentrically held condition, the flatness of the sheet 2 is adversely affected, and the sheet 2 is subject to flapping motion during rotation. So that the sheet 2 can be correctly positioned on the peripheral edge portion of the circular recess 3a, as shown in FIG. 4, as the collet 4 is moved down, it is desirable that the coefficient of friction of the sheet 2 with respect to the rotatable section 3 and the collet 4 be low.